As lung volume increases, what happens to its internal pressure?

When lung volume increases, the internal pressure within the lungs decreases. This phenomenon can be explained by Boyle's Law, which establishes the relationship between the pressure and volume of a gas at constant temperature. According to Boyle's Law, as the volume of a gas increases, the pressure it exerts decreases, provided the temperature remains constant.

In the context of respiration, when the diaphragm and intercostal muscles contract, the thoracic cavity's volume increases. As the lungs expand, the air inside them fills a larger space, leading to a reduction in internal lung pressure relative to atmospheric pressure. This drop in pressure creates a pressure gradient that allows air to flow into the lungs from the outside environment, enabling inhalation. Thus, as lung volume expands, the internal pressure decreases, facilitating the process of breathing.